Ultrasound apparatuses for thermally-induced renal neuromodulation and associated systems and methods

ABSTRACT

Methods and apparatus are provided for thermally-induced renal neuromodulation. Thermally-induced renal neuromodulation may be achieved via direct and/or via indirect application of thermal energy to heat or cool neural fibers that contribute to renal function, or of vascular structures that feed or perfuse the neural fibers. In some embodiments, parameters of the neural fibers, of non-target tissue, or of the thermal energy delivery element, may be monitored via one or more sensors for controlling the thermally-induced neuromodulation. In some embodiments, protective elements may be provided to reduce a degree of thermal damage induced in the non-target tissues.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/754,337, filed Apr. 5, 2010, which is a continuation of U.S.patent application Ser. No. 11/840,142, filed Aug. 16, 2007, now U.S.Pat. No. 7,717,948, which is a continuation of U.S. patent applicationSer. No. 11/504,117, filed Aug. 14, 2006, now U.S. Pat. No. 7,617,005,which claims the benefit of U.S. Provisional Application No. 60/816,999filed on Jun. 28, 2006. U.S. patent application Ser. No. 11/504,117,filed Aug. 14, 2006, now U.S. Pat. No. 7,617,005 is also aContinuation-In-Part application of each of the following:

(A) U.S. patent application Ser. No. 10/408,665, filed on Apr. 8, 2003,now U.S. Pat. No. 7,162,303, which claims the benefit of U.S.Provisional Application Nos. 60/370,190, filed on Apr. 8, 2002,60/415,575, filed on Oct. 3, 2002, and 60/442,970, filed on Jan. 29,2003.

(B) U.S. patent application Ser. No. 11/189,563, filed on Jul. 25, 2005,now U.S. Pat. No. 8,145,316, which is a Continuation-In-Part applicationof U.S. patent application Ser. No. 11/129,765, filed on May 13, 2005,now U.S. Pat. No. 7,653,438, which claims the benefit of U.S.Provisional Application Nos. 60/616,254, filed on Oct. 5, 2004, and60/624,793, filed on Nov. 2, 2004.

All of these applications are incorporated herein by reference in theirentireties.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

TECHNICAL FIELD

The present invention relates to methods and apparatus forneuromodulation. More particularly, the present invention relates tomethods and apparatus for achieving renal neuromodulation via thermalheating and/or cooling mechanisms.

BACKGROUND

Congestive Heart Failure (“CHF”) is a condition that occurs when theheart becomes damaged and reduces blood flow to the organs of the body.If blood flow decreases sufficiently, kidney function becomes altered,which results in fluid retention, abnormal hormone secretions andincreased constriction of blood vessels. These results increase theworkload of the heart and further decrease the capacity of the heart topump blood through the kidneys and circulatory system.

It is believed that progressively decreasing perfusion of the kidneys isa principal non-cardiac cause perpetuating the downward spiral of CHF.Moreover, the fluid overload and associated clinical symptoms resultingfrom these physiologic changes result in additional hospital admissions,poor quality of life and additional costs to the health care system.

In addition to their role in the progression of CHF, the kidneys play asignificant role in the progression of Chronic Renal Failure (“CRF”),End-Stage Renal Disease (“ESRD”), hypertension (pathologically highblood pressure) and other cardio-renal diseases. The functions of thekidneys can be summarized under three broad categories: filtering bloodand excreting waste products generated by the body's metabolism;regulating salt, water, electrolyte and acid-base balance; and secretinghormones to maintain vital organ blood flow. Without properlyfunctioning kidneys, a patient will suffer water retention, reducedurine flow and an accumulation of waste toxins in the blood and body.These conditions result from reduced renal function or renal failure(kidney failure) and are believed to increase the workload of the heart.In a CHF patient, renal failure will cause the heart to furtherdeteriorate as fluids are retained and blood toxins accumulate due tothe poorly functioning kidneys.

It has been established in animal models that the heart failurecondition results in abnormally high sympathetic activation of thekidneys. An increase in renal sympathetic nerve activity leads todecreased removal of water and sodium from the body, as well asincreased renin secretion. Increased renin secretion leads tovasoconstriction of blood vessels supplying the kidneys, which causesdecreased renal blood flow. Reduction of sympathetic renal nerveactivity, e.g., via denervation, may reverse these processes.

Applicants have previously described methods and apparatus for treatingrenal disorders by applying a pulsed electric field to neural fibersthat contribute to renal function. See, for example, Applicants' U.S.Pat. Nos. 7,653,438, 8,145,316, and 7,620,451, all of which areincorporated herein by reference in their entireties. A pulsed electricfield (“PEF”) may initiate renal neuromodulation, e.g., denervation, forexample, via irreversible electroporation or via electrofusion. The PEFmay be delivered from apparatus positioned intravascularly,extravascularly, intra-to-extravascularly or a combination thereof.Additional methods and apparatus for achieving renal neuromodulation,e.g., via localized drug delivery (such as by a drug pump or infusioncatheter) or via use of a stimulation electric field, etc, aredescribed, for example, in Applicants' U.S. Pat. Nos. 7,162,303 and6,978,174, both of which are incorporated herein by reference in theirentireties.

A potential challenge of using PEF systems for treating renal disordersis to selectively electroporate target cells without affecting othercells. For example, it may be desirable to irreversibly electroporaterenal nerve cells that travel along or in proximity to renalvasculature, but it may not be desirable to damage the smooth musclecells of which the vasculature is composed. As a result, an overlyaggressive course of PEF therapy may persistently injure the renalvasculature, but an overly conservative course of PEF therapy may notachieve the desired renal neuromodulation.

Applicants have previously described methods and apparatus formonitoring changes in tissue impedance or conductivity in order todetermine the effects of pulsed electric field therapy, e.g., todetermine an extent of electroporation and/or its degree ofirreversibility. See, for example, Applicants' co-pending U.S. PatentApplication Publication No. US 2007/0083239, which is incorporatedherein by reference in its entirety. However, in some patients it may bedifficult or impractical to achieve such real-time monitoring whenutilizing pulsed electric field neuromodulatory mechanisms. In somepatients, this may necessitate re-intervention should it be establishedafter the procedure that a degree of induced neuromodulation was notsufficient to achieve a desired treatment outcome. Thus, it would bedesirable to achieve renal neuromodulation via more easily monitoredand/or controlled neuromodulatory mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a schematic view illustrating human renal anatomy.

FIG. 2 is a schematic isometric detail view showing the location of therenal nerves relative to the renal artery.

FIG. 3 is a schematic side view, partially in section, illustrating anexample of an extravascular method and apparatus for thermal renalneuromodulation.

FIGS. 4A and 4B are schematic side views, partially in section,illustrating examples of intravascular methods and apparatus for thermalrenal neuromodulation.

FIGS. 5A and 5B are schematic side views, partially in section,illustrating an alternative embodiment of the intravascular methods andapparatus of FIG. 4 comprising wall-contacting electrodes.

FIGS. 6A and 6B are schematic side views, partially in section,illustrating an additional alternative embodiment of the intravascularmethods and apparatus of FIG. 4 comprising alternative wall-contactingelectrodes.

FIGS. 7A and 7B are schematic side views, partially in section,illustrating other alternative embodiments of the intravascular methodsand apparatus of FIG. 4 comprising multiple wall-contacting electrodes.

FIG. 8 is a schematic side view, partially in section, illustrating anexample of an intra-to-extravascular method and apparatus for thermalrenal neuromodulation.

FIG. 9 is a schematic side view, partially in section, of an alternativeembodiment of the method and apparatus of FIG. 8 configured for thermalrenal neuromodulation via direct application of thermal energy.

FIG. 10 is a schematic side view, partially in section, illustrating amethod and apparatus for thermal renal neuromodulation comprising athermoelectric element suitable for direct application of thermal energyto target neural fibers.

FIG. 11 is a schematic side view, partially in section, illustratinganother method and apparatus for thermal renal neuromodulationcomprising a thermoelectric element.

FIGS. 12A and 12B are schematic side views, partially in section,illustrating a method and apparatus for thermal renal neuromodulationvia high-intensity focused ultrasound.

FIG. 13 is a schematic side view, partially in section, illustrating analternative embodiment of the apparatus and method of FIG. 12.

FIGS. 14A and 14B are schematic diagrams for classifying the varioustypes of thermal neuromodulation that may be achieved with the apparatusand methods of the present invention.

DETAILED DESCRIPTION A. Overview

The present invention provides methods and apparatus for renalneuromodulation via thermal heating and/or thermal cooling mechanisms,e.g., to achieve a reduction in renal sympathetic nerve activity.Thermally-induced (via heating and/or cooling) neuromodulation may beachieved via apparatus positioned proximate target neural fibers, forexample, positioned within renal vasculature (i.e., positionedintravascularly), positioned extravascularly, positionedintra-to-extravascularly or a combination thereof. Thermalneuromodulation by either heating or cooling may be due to direct effectto, or alteration of, the neural structures that is induced by thethermal stress. Additionally or alternatively, the thermalneuromodulation may at least in part be due to alteration of vascularstructures, e.g., arteries, arterioles, capillaries or veins, whichperfuse the target neural fibers or surrounding tissue. Furtherstill,the modulation may at least in part be due to electroporation of thetarget neural fibers or of surrounding tissue.

As used herein, thermal heating mechanisms for neuromodulation includeboth thermal ablation and non-ablative thermal injury or damage (e.g.,via sustained heating or resistive heating). Thermal heating mechanismsmay include raising the temperature of target neural fibers above adesired threshold, for example, above a body temperature of about 37°C., e.g., to achieve non-ablative thermal injury, or above a temperatureof about 45° C. (e.g., above about 60° C.) to achieve ablative thermalinjury.

As used herein, thermal cooling mechanisms for neuromodulation includenon-freezing thermal slowing of nerve conduction and/or non-freezingthermal nerve injury, as well as freezing thermal nerve injury. Thermalcooling mechanisms may include reducing the temperature of target neuralfibers below a desired threshold, for example, below the bodytemperature of about 37° C. (e.g., below about 20° C.) to achievenon-freezing thermal injury. Thermal cooling mechanisms also may includereducing the temperature of the target neural fibers below about 0° C.,e.g., to achieve freezing thermal injury.

In addition to monitoring or controlling the temperature during thermalneuromodulation, a length of exposure to thermal stimuli may bespecified to affect an extent or degree of efficacy of the thermalneuromodulation. The length of exposure to thermal stimuli is longerthan instantaneous exposure, such as longer than about 30 seconds, oreven longer than 2 minutes. Furthermore, the length of exposure can beless than 10 minutes, though this should in no way be construed as theupper limit of the exposure period. Exposure times measured in hours,days or longer, may be utilized to achieve desired thermalneuromodulation.

When conducting neuromodulation via thermal mechanisms, the temperaturethreshold discussed previously may be determined as a function of theduration of exposure to thermal stimuli. Additionally or alternatively,the length of exposure may be determined as a function of the desiredtemperature threshold. These and other parameters may be specified orcalculated to achieve and control desired thermal neuromodulation.

In some embodiments, thermally-induced renal neuromodulation may beachieved via direct application of thermal cooling or heating energy tothe target neural fibers. For example, a chilled or heated fluid can beapplied at least proximate to the target neural fiber, or heated orcooled elements (e.g., a thermoelectric element or a resistive heatingelement) can be placed in the vicinity of the neural fibers. In otherembodiments, thermally-induced renal neuromodulation may be achieved viaindirect generation and/or application of the thermal energy to thetarget neural fibers, such as through application of a ‘thermal’electric field, of high-intensity focused ultrasound, of laserirradiation, etc., to the target neural fibers. For example,thermally-induced renal neuromodulation may be achieved via delivery ofa pulsed or continuous thermal electric field to the target neuralfibers, the electric field being of sufficient magnitude and/or durationto thermally induce the neuromodulation in the target fibers (e.g., toheat or thermally ablate or necrose the fibers). Additional andalternative methods and apparatus may be utilized to achievethermally-induced renal neuromodulation, as described hereinafter.

When utilizing thermal heating mechanisms for thermal neuromodulation,protective cooling elements, such as convective cooling elements,optionally may be utilized to protect smooth muscle cells or othernon-target tissue from thermal damage during the thermally-induced renalneuromodulation. Likewise, when utilizing thermal cooling mechanisms,protective heating elements, such as convective heating elements, may beutilized to protect the non-target tissue. When thermal neuromodulationis achieved via thermal energy delivered intravascularly, the non-targettissue may be protected by utilizing blood flow as a conductive and/orconvective heat sink that carries away excess thermal energy (hot orcold). For example, when blood flow is not blocked, the circulatingblood may provide a relatively constant temperature medium for removingthe excess thermal energy from the non-target tissue during theprocedure. The non-target tissue additionally or alternatively may beprotected by focusing the thermal heating or cooling energy on thetarget neural fibers such that an intensity of the thermal energy isinsufficient to induce the thermal damage in the non-target tissuedistant from the target neural fibers.

In some embodiments, methods and apparatus for real-time monitoring ofan extent or degree of neuromodulation or denervation (e.g., an extentor degree of thermal damage) in the target neural fibers and/or ofthermal damage in the non-target tissue may be provided. Likewise,real-time monitoring of the thermal energy delivery element may beprovided. Such methods and apparatus may, for example, comprise athermocouple or other temperature sensor for measuring the temperatureof the monitored tissue or of the thermal energy delivery element. Poweror total energy delivered additionally or alternatively may bemonitored.

To better understand the structures of devices of the present inventionand the methods of using such devices for thermally-induce renalneuromodulation, it is instructive to examine the renal anatomy inhumans.

B. Renal Anatomy Summary

With reference to FIG. 1, the human renal anatomy includes the kidneysK, which are supplied with oxygenated blood by the renal arteries RA.The renal arteries are connected to the heart via the abdominal aortaAA. Deoxygenated blood flows from the kidneys to the heart via the renalveins RV and the inferior vena cava IVC.

FIG. 2 illustrates a portion of the renal anatomy in greater detail.More specifically, the renal anatomy also includes renal nerves RNextending longitudinally along the lengthwise dimension L of renalartery RA, generally within the adventitia of the artery. The renalartery RA has smooth muscle cells SMC that surround the arterialcircumference and spiral around the angular axis θ of the artery. Thesmooth muscle cells of the renal artery accordingly have a lengthwise orlonger dimension extending transverse (i.e., non-parallel) to thelengthwise dimension of the renal artery. The misalignment of thelengthwise dimensions of the renal nerves and the smooth muscle cells isdefined as “cellular misalignment.”

C. Embodiments of Apparatus and Methods for Neuromodulation

FIGS. 3-13 illustrate examples of systems and methods forthermally-induced renal neuromodulation. FIG. 3 shows one embodiment ofan extravascular apparatus 200 that includes one or more electrodesconfigured to deliver a thermal electric field to renal neural fibers inorder to achieve renal neuromodulation via heating. The apparatus ofFIG. 3 is configured for temporary extravascular placement; however, itshould be understood that partially or completely implantableextravascular apparatus additionally or alternatively may be utilized.Applicants have previously described extravascular pulsed electric fieldsystems, for example, in Applicants' U.S. Pat. No. 8,145,316, which hasbeen incorporated herein by reference in its entirety.

In FIG. 3, apparatus 200 comprises a laparoscopic or percutaneous systemhaving a probe 210 configured for insertion in proximity to the track ofthe renal neural supply along the renal artery or vein or hilum and/orwithin Gerota's fascia under, e.g., CT or radiographic guidance. Atleast one electrode 212 is configured for delivery through the probe 210to a treatment site for delivery of a thermal electric field therapy.The electrode(s) 212, for example, may be mounted on a catheter andelectrically coupled to a thermal electric field generator 50 via wires211. In an alternative embodiment, a distal section of the probe 210 mayhave at least one electrode 212, and the probe may have an electricalconnector to couple the probe to the field generator 50 for delivering athermal electric field to the electrode(s) 212.

The field generator 50 is located external to the patient. Thegenerator, as well as any of the electrode embodiments described herein,may be utilized with any embodiment of the present invention fordelivery of a thermal electric field with desired field parameters,e.g., parameters sufficient to thermally or otherwise induce renalneuromodulation in target neural fibers via heating and/orelectroporation. It should be understood that electrodes of embodimentsdescribed hereinafter may be electrically connected to the generatoreven though the generator is not explicitly shown or described with eachembodiment. Furthermore, the field generator optionally may bepositioned internal to the patient. Furtherstill, the field generatormay additionally comprise or may be substituted with an alternativethermal energy generator, such as a thermoelectric generator for heatingor cooling (e.g., a Peltier device), or a thermal fluid injection systemfor heating or cooling, etc.

The electrode(s) 212 can be individual electrodes that are electricallyindependent of each other, a segmented electrode with commonly connectedcontacts, or a continuous electrode. A segmented electrode may, forexample, be formed by providing a slotted tube fitted onto theelectrode, or by electrically connecting a series of individualelectrodes. Individual electrodes or groups of electrodes 212 may beconfigured to provide a bipolar signal. The electrodes 212 may bedynamically assignable to facilitate monopolar and/or bipolar energydelivery between any of the electrodes and/or between any of theelectrodes and an external ground pad. Such a ground pad may, forexample, be attached externally to the patient's skin, e.g., to thepatient's leg or flank. In FIG. 3, the electrodes 212 comprise a bipolarelectrode pair. The probe 210 and the electrodes 212 may be similar tothe standard needle or trocar-type used clinically for RF nerve block.Alternatively, the apparatus 200 may comprise a flexible and/orcustom-designed probe for the renal application described herein.

In FIG. 3, the percutaneous probe 210 has been advanced through apercutaneous access site P into proximity with a patient's renal arteryRA. The probe pierces the patient's Gerota's fascia F, and theelectrodes 212 are advanced into position through the probe and alongthe annular space between the patient's artery and fascia. Once properlypositioned, the target neural fibers may be heated via a pulsed orcontinuous electric field delivered across the bipolar electrodes 212.Such heating may, for example, ablate or cause non-ablative thermalinjury to the target neural fibers, thereby at least partiallydenervating the kidney innervated by the target neural fibers. Theelectric field also may induce reversible or irreversibleelectroporation in the target neural fibers, which may compliment thethermal injury induced in the neural fibers. After treatment, theapparatus 200 may be removed from the patient to conclude the procedure.

Referring now to FIGS. 4A and 4B, embodiments of intravascular systemsfor thermally-induced renal neuromodulation is described. Applicantshave previously described intravascular pulsed electric field systems,for example, in U.S. Pat. No. 7,653,438, which has been incorporatedherein by reference in its entirety. The embodiments of FIG. 4 includean apparatus 300 comprising a catheter 302 having an optionalpositioning element 304 (e.g., a balloon, an expandable wire basket,other mechanical expanders, etc.), shaft electrodes 306 a and 306 bdisposed along the shaft of the catheter, and optional radiopaquemarkers 308 disposed along the shaft of the catheter in the region ofthe positioning element 304. The electrodes 306 a-b, for example, can bearranged such that the electrode 306 a is near a proximal end of thepositioning element 304 and the electrode 306 b is near the distal endof the positioning element 304. The electrodes 306 are electricallycoupled to the field generator 50 (see FIG. 3), which is disposedexternal to the patient, for delivery of a thermal electric field forheating of target neural fibers. In an alternative embodiment, one ormore of the electrodes may comprise Peltier electrodes for cooling thetarget neural fibers to modulate the fibers.

The positioning element 304 optionally may center or otherwise positionthe electrodes 306 a and 306 b within a vessel. Additionally, as in FIG.4A, the positioning element may comprise an impedance-altering elementthat alters the impedance between electrodes 306 a and 306 b during thetherapy, for example, to better direct the thermal electric field acrossthe vessel wall. This may reduce an energy required to achieve desiredrenal neuromodulation and may reduce a risk of injury to non-targettissue. Applicants have previously described use of a suitableimpedance-altering element in Applicants' U.S. Pat. No. 7,756,583, whichis incorporated herein by reference in its entirety. When thepositioning element 304 comprises an inflatable balloon as in FIG. 4A,the balloon may serve as both a centering element for the electrodes 306and as an impedance-altering electrical insulator for directing anelectric field delivered across the electrodes, e.g., for directing theelectric field into or across the vessel wall for modulation of targetneural fibers. Electrical insulation provided by the positioning element304 may reduce the magnitude of applied energy or other parameters ofthe thermal electric field necessary to achieve desired heating at thetarget fibers.

Furthermore, the positioning element 304 optionally may be utilized as acooling element and/or a heating element. For example, the positioningelement 304 may be inflated with a chilled fluid that serves as a heatsink for removing heat from tissue that contacts the element.Conversely, the positioning element 304 optionally may be a heatingelement by inflating it with a warmed fluid that heats tissue in contactwith the element. The thermal fluid optionally may be circulated and/orexchanged within the positioning element 304 to facilitate moreefficient conductive and/or convective heat transfer. Thermal fluidsalso may be used to achieve thermal neuromodulation via thermal coolingor heating mechanisms, as described in greater detail herein below. Thepositioning element 304 (or any other portion of apparatus 300)additionally or alternatively may comprise one or more sensors formonitoring the process. In one embodiment, the positioning element 304has a wall-contacting thermocouple 310 (FIG. 4A) for monitoring thetemperature or other parameters of the target tissue, the non-targettissue, the electrodes, the positioning element and/or any other portionof the apparatus 300.

The electrodes 306 can be individual electrodes (i.e., independentcontacts), a segmented electrode with commonly connected contacts, or asingle continuous electrode. Furthermore, the electrodes 306 may beconfigured to provide a bipolar signal, or the electrodes 306 may beused together or individually in conjunction with a separate patientground pad for monopolar use. As an alternative or in addition toplacement of the electrodes 306 along the central shaft of the catheter302, as in FIG. 4, the electrodes 306 may be attached to the positioningelement 304 such that they contact the wall of the renal artery RA. Insuch a variation, the electrodes may, for example, be affixed to theinside surface, outside surface or at least partially embedded withinthe wall of the positioning element. FIG. 5 illustrate alternativewall-contacting electrodes.

In use, the catheter 302 may be delivered to the renal artery RA asshown, or it may be delivered to a renal vein or to any other vessel inproximity to neural tissue contributing to renal function, in a lowprofile delivery configuration through a guide catheter or other device.Alternatively, catheters may be positioned in multiple vessels forthermal renal neuromodulation, e.g., within both the renal artery andthe renal vein. Multi-vessel techniques for pulsed electric field renalneuromodulation have been described previously, for example, inApplicants' U.S. Pat. No. 7,853,333, which is incorporated herein byreference in its entirety.

Once positioned within the renal vasculature as desired, the optionalpositioning element 304 may be expanded into contact with an interiorwall of the vessel. A thermal electric field then may be generated bythe field generator 50, transferred through the catheter 302 to theelectrodes 306, and delivered via the electrodes 306 across the wall ofthe artery. The electric field thermally modulates the activity alongneural fibers that contribute to renal function via heating. In severalembodiments, the thermal modulation at least partially denervates thekidney innervated by the neural fibers via heating. This may beachieved, for example, via thermal ablation or via non-ablative damageof the target neural fibers. The electric field also may induceelectroporation in the neural fibers.

In the embodiment of FIG. 4A, the positioning element 304 illustrativelycomprises an inflatable balloon, which may preferentially direct theelectric field as discussed. In the embodiment of FIG. 4B, thepositioning element comprises an expandable wire basket thatsubstantially centers the electrodes 306 within the vessel withoutblocking blood flow through the vessel. During delivery of the thermalelectric field (or of other thermal energy), the blood may act as a heatsink for conductive and/or convective heat transfer for removing excessthermal energy from the non-target tissue, thereby protecting thenon-target tissue. This effect may be enhanced when blood flow is notblocked during energy delivery, as in the embodiment of FIG. 4B.

Use of the patient's blood as a heat sink is expected to facilitatedelivery of longer or higher energy thermal treatments with reduced riskof damage to the non-target tissue, which may enhance the efficacy ofthe treatment at the target neural fibers. Although the embodiment ofFIG. 4B illustratively comprises a positioning element for centering theelectrodes without blocking flow, it should be understood that thepositioning element may be eliminated and/or that the electrodes may beattached to the positioning element such that they are not centered inthe vessel upon expansion of the centering element. In such embodiments,the patient's blood may still mitigate excess thermal heating or coolingto protect non-target tissues.

In addition or as an alternative to utilizing the patient's blood as aheat sink, a thermal fluid (hot or cold) may be injected into the vesselto remove excess thermal energy and protect the non-target tissues. Thethermal fluid may, for example, be injected through the device catheteror through a guide catheter at a location upstream from an energydelivery element or at other locations relative to the tissue for whichprotection is sought. Furthermore, this method of using an injectedthermal fluid to remove excess thermal energy from non-target tissues toprotect the non-target tissues from thermal injury during therapeutictreatment of target tissues may be utilized in body lumens other thanblood vessels.

One or more sensors, such as the thermocouple 310 of FIG. 4A, may beused to monitor the temperature(s) or other parameter(s) at theelectrodes 306, at the wall of the vessel and/or at other desiredlocations along the apparatus or the patient's anatomy. The thermalneuromodulation may be controlled using the measured parameter(s) asfeedback. This feedback may be used, for example, to maintain theparameter(s) below a desired threshold. For example, the parameter(s)may be maintained below a threshold that may cause injury to thenon-target tissues. With blood flowing through the vessel, more thermalenergy may be carried away, which may allow for longer or higher energytreatments than when blood flow is blocked in the vessel.

As discussed, when utilizing intravascular apparatus to achieve thermalneuromodulation, in addition or as an alternative to central positioningof the electrode(s) within a blood vessel, the electrode(s) optionallymay be configured to contact an internal wall of the blood vessel.Wall-contacting electrode(s) may facilitate more efficient transfer of athermal electric field across the vessel wall to target neural fibers,as compared to centrally-positioned electrode(s). In some embodiments,the wall-contacting electrode(s) may be delivered to the vesseltreatment site in a reduced profile configuration, then expanded in vivoto a deployed configuration wherein the electrode(s) contact the vesselwall. In some embodiments, expansion of the electrode(s) is at leastpartially reversible to facilitate retrieval of the electrode(s) fromthe patient's vessel.

FIGS. 5A and 5B depict an illustrative embodiment of intravascularapparatus having electrodes configured to contact the interior wall of avessel. The apparatus of FIGS. 5A and 5B is an alternative embodiment ofthe apparatus 300 of FIGS. 4A and 4B wherein the proximal electrode 306a of FIGS. 4A and 4B has been replaced with wall-contacting electrode306 a′. The wall-contacting electrode comprises proximal attachment 312a that connects the electrode to the shaft of the catheter 302 and iselectrically coupled to the pulse generator. Extensions 314 a extendfrom proximal attachment 312 a and at least partially extend over asurface of positioning element 304. The extensions 314 a optionally maybe selectively insulated such that only a selective portion of theextensions, e.g., the distal tips of the extensions, are electricallyactive. The electrode 306 a′ optionally may be fabricated from a slottedtube, such as a stainless steel or shape-memory (e.g., NiTi) slottedtube. Furthermore, all or a portion of the electrode may be gold-platedto improve radiopacity and/or conductivity.

As seen in FIG. 5A, catheter 302 may be delivered over a guidewire G toa treatment site within the patient's vessel with the electrode 306 a′positioned in a reduced profile configuration. Catheter 302 optionallymay be delivered through a guide catheter 303 to facilitate such reducedprofile delivery of the wall-contacting electrode. When positioned asdesired at a treatment site, the electrode may be expanded into contactwith the vessel wall by expanding the optional positioning element 304,as in FIG. 5B. A thermal monopolar or bipolar electric field then may bedelivered across the vessel wall and between the electrodes 306 a′ and306 b to induce thermal neuromodulation, as discussed previously. Theoptional positioning element 304 may alter impedance within the bloodvessel and more efficiently route the electrical energy across thevessel wall to the target neural fibers.

After delivery of the electric field, the electrode 306 a′ may bereturned to a reduced profile to facilitate removal of the apparatus 300from the patient. For example, the positioning element 304 may becollapsed (e.g., deflated), and the electrode 306 a′ may be contractedby withdrawing the catheter 302 within the guide catheter 303.Alternatively, the electrode may be fabricated from a shape-memorymaterial biased to the collapsed configuration, such that the electrodeself-collapses upon collapse of the positioning element.

Although in FIGS. 5A and 5B the electrode 306 a′ is expanded intocontact with the vessel wall, it should be understood that the electrodealternatively may be fabricated from a self-expanding material biasedsuch that the electrode self-expands into contact with the vessel wallupon positioning of the electrode distal of the guide catheter 303. Aself-expanding embodiment of the electrode 306 a′ may obviate a need forthe positioning element 304 and/or may facilitate maintenance of bloodflow through the blood vessel during delivery of an electric field viathe electrode. After delivery of the electric field, the self-expandingelectrode 306 a′ may be returned to a reduced profile to facilitateremoval of the apparatus 300 from the patient by withdrawing thecatheter 302 within the guide catheter 303.

FIGS. 6A and 6B depict another embodiment of the apparatus and methodsof FIGS. 4A and 4B comprising a wall-contacting electrode. As analternative to the proximal attachment 312 a of electrode 306 a′ ofFIGS. 5A and 5B, the electrode 306 a″ of FIG. 6 comprises distalattachment 316 a for coupling the electrode to the shaft of catheter 302on the distal side of the positioning element 304. Distal attachment ofthe electrode allows the electrode to extend over the entirety of thepositioning element 304 and may facilitate contraction of the electrode306 a″ after thermal neuromodulation. For example, the electrode 306 a″can be contracted by proximally retracting the extensions 312 a relativeto the catheter 302 during or after contraction of the positioningelement 304. FIG. 6A shows the electrode 306 a″ in the reduced profileconfiguration, while FIG. 6B shows the electrode in the expanded,wall-contacting configuration.

FIGS. 7A and 7B show additional alternative embodiments of the methodsand apparatus of FIGS. 4A and 4B. In FIGS. 7A and 7B, the apparatus 300comprises both the proximal electrode 306 a′ of FIGS. 5A and 5B, as wellas a wall-contacting distal electrode 306 b′. The embodiment of FIG. 7Acomprises proximal and distal positioning elements 304 a and 304 b,respectively, for expanding the proximal and distal wall-contactingelectrodes 306 a′ and 306 b′, respectively, into contact with the vesselwall. The embodiment of FIG. 7B comprises only a single positioningelement 304, but the distal wall-contacting electrode 306 b′ is proximalfacing and positioned over the distal portion of the positioning element304 to facilitate expansion of the distal electrode 306 b′. In theembodiment of FIG. 7B, the extensions of the proximal and distalelectrodes optionally may be connected along non-conductive connectors318 to facilitate collapse and retrieval of the electrodespost-treatment.

A bipolar electric field may be delivered between the proximal anddistal wall-contacting electrodes, or a monopolar electric field may bedelivered between the proximal and/or distal electrode(s) and anexternal ground. Having both the proximal and distal electrodes incontact with the wall of the vessel may facilitate more efficient energytransfer across the wall during delivery of a thermal electric field, ascompared to having one or both of the proximal and distal electrodescentered within the vessel.

In addition to extravascular and intravascular systems forthermally-induced renal neuromodulation, intra-to-extravascular systemsmay be provided. The intra-to-extravascular systems may, for example,have electrode(s) that are delivered to an intravascular position, andthen at least partially passed through/across the vessel wall to anextravascular position prior to delivery of a thermal electric field.Intra-to-extravascular positioning of the electrode(s) may place theelectrode(s) in closer proximity to target neural fibers for delivery ofa thermal electric field, as compared to fully intravascular positioningof the electrode(s). Applicants have previously describedintra-to-extravascular pulsed electric field systems, for example, inApplicants' U.S. Pat. No. 7,620,451, which is incorporated herein byreference in its entirety.

With reference to FIG. 8, one embodiment of an intra-to-extravascular(“ITEV”) system for thermally-induced renal neuromodulation isdescribed. ITEV system 320 comprises a catheter 322 having (a) aplurality of proximal electrode lumens terminating at proximal sideports 324, (b) a plurality of distal electrode lumens terminating atdistal side ports 326, and (c) a guidewire lumen 323. The catheter 322preferably comprises an equal number of proximal and distal electrodelumens and side ports. The system 320 also includes proximal needleelectrodes 328 that may be advanced through the proximal electrodelumens and the proximal side ports 324, as well as distal needleelectrodes 329 that may be advanced through the distal electrode lumensand the distal side ports 326.

Catheter 322 comprises an optional expandable positioning element 330,which may comprise an inflatable balloon or an expandable basket orcage. In use, the positioning element 330 may be expanded prior todeployment of the needle electrodes 328 and 329 in order to position orcenter the catheter 322 within the patient's vessel (e.g., within renalartery RA). Centering the catheter 322 is expected to facilitatedelivery of all needle electrodes to desired depths within/external tothe patient's vessel (e.g., to deliver all of the needle electrodesapproximately to the same depth). In FIG. 8, the illustrated positioningelement 330 is positioned between the proximal side ports 324 and thedistal side ports 326, i.e., between the delivery positions of theproximal and distal electrodes. However, it should be understood thatthe positioning element 330 additionally or alternatively may bepositioned at a different location or at multiple locations along thelength of the catheter 322 (e.g., at a location proximal of the sideports 324 and/or at a location distal of the side ports 326).

As illustrated in FIG. 8, the catheter 322 may be advanced to atreatment site within the patient's vasculature (e.g., to a treatmentsite within the patient's renal artery RA) over a guidewire (not shown)via the lumen 323. During intravascular delivery, the electrodes 328 and329 may be positioned such that their non-insulated and sharpened distalregions are positioned within the proximal and distal lumens,respectively. Once positioned at a treatment site, a medicalpractitioner may advance the electrodes via their proximal regions thatare located external to the patient. Such advancement causes the distalregions of the electrodes 328 and 329 to exit side ports 324 and 326,respectively, and pierce the wall of the patient's vasculature such thatthe electrodes are positioned extravascularly via an ITEV approach.

The proximal electrodes 328 can be connected to electric field generator50 as active electrodes, and the distal electrodes 329 can serve asreturn electrodes. In this manner, the proximal and distal electrodesform bipolar electrode pairs that align the thermal electric field witha longitudinal axis or direction of the patient's vasculature. As willbe apparent, the distal electrodes 329 alternatively may comprise theactive electrodes and the proximal electrodes 328 may comprise thereturn electrodes. Furthermore, the proximal and/or the distalelectrodes may comprise both active and return electrodes. Furtherstill,the proximal and/or the distal electrodes may be utilized in combinationwith an external ground for delivery of a monopolar thermal electricfield. Any combination of active and distal electrodes may be utilized,as desired.

When the electrodes 328 and 329 are connected to generator 50 andpositioned extravascularly, and with the positioning element 330optionally expanded, delivery of the thermal electric field may proceedto achieve desired renal neuromodulation via heating. The electric fieldalso may induce electroporation. After achievement of thethermally-induced renal neuromodulation, the electrodes may be retractedwithin the proximal and distal lumens, and the positioning element 330may be collapsed for retrieval. ITEV system 320 then may be removed fromthe patient to complete the procedure. Additionally or alternatively,the system may be repositioned to provide therapy at another treatmentsite, such as to provide bilateral renal neuromodulation.

As discussed previously, cooling elements, such as convective coolingelements, may be utilized to protect non-target tissues like smoothmuscle cells from thermal damage during thermally-induced renalneuromodulation via heat generation. Non-target tissues additionally oralternatively may be protected by focusing the thermal energy on thetarget neural fibers such that an intensity of the thermal energy isinsufficient to induce thermal damage in non-target tissues distant fromthe target neural fibers.

Although FIGS. 3-8 illustratively show bipolar apparatus, it should beunderstood that monopolar apparatus alternatively may be utilized. Forexample, an active monopolar electrode may be positionedintravascularly, extravascularly or intra-to-extravascularly inproximity to target neural fibers that contribute to renal function. Areturn electrode ground pad may be attached to the exterior of thepatient. Finally, a thermal electric field may be delivered between thein vivo monopolar electrode and the ex vivo ground pad to effectuatedesired thermally-induced renal neuromodulation. Monopolar apparatusadditionally may be utilized for bilateral renal neuromodulation.

The embodiments of FIGS. 3-8 illustratively describe methods andapparatus for thermally-induced renal neuromodulation via delivery ofthermal electric fields that modulate the target neural fibers. However,it should be understood that alternative methods and apparatus forthermally-induced (via both heating and cooling) renal neuromodulationmay be provided. For example, electric fields may be used to cool andmodulate the neural fibers, e.g., via thermoelectric or Peltierelements. Thermally-induced renal neuromodulation optionally may beachieved via direct application of thermal energy to the target neuralfibers. Such direct thermal energy may be generated and/or transferredin a variety of ways, such as via resistive heating, via delivery of aheated or chilled fluid (see FIGS. 9 and 11), via a Peltier element (seeFIG. 10), etc. Thermally-induced renal neuromodulation additionally oralternatively may be achieved via application of high-intensity focusedultrasound to the target neural fibers (see FIG. 12). Additional andalternative methods and apparatus for thermally-induced renalneuromodulation may be used in accordance with the present invention.

With reference now to FIG. 9, an alternative embodiment of the apparatusand methods of FIG. 8 is described that is configured forthermally-induced neuromodulation via direct application of thermalenergy. In the embodiment of FIG. 9, the electrodes 328 and 329 of FIG.8 have been replaced with infusion needles 328′ and 329′, respectively.A thermal fluid F may be delivered through the needles to the targetneural fibers. The thermal fluid may be heated in order to raise thetemperature of the target neural fibers above a desired threshold. Forexample, the temperature of the neural fibers can be raised above a bodytemperature of about 37° C., or above a temperature of about 45° C.Alternatively, the thermal fluid may be chilled to reduce thetemperature of the target neural fibers below a desired threshold. Forexample, the neural fibers can be cooled to below the body temperatureof about 37° C., or further cooled below about 20° C., or still furthercooled below a freezing temperature of about 0° C. As will be apparent,in addition to intra-to-extravascular delivery of a thermal fluid, thethermal fluid may be delivered intravascularly (e.g., may inflate and/orbe circulated through a balloon member), extravascularly (e.g., may becirculated through a vascular cuff) or a combination thereof.

In addition or as alternative to injection of a thermal fluid to thetarget neural fibers through infusion needles 328′ and 329′, analternative neuromodulatory agent, such as a drug or medicament, may beinjected to modulate, necrose or otherwise block or reduce transmissionalong the target neural fibers. Examples of alternative neuromodulatoryagents include, but are not limited to, phenol and neurotoxins, such asbotulinum toxin. Additional neuromodulatory agents, per se known, willbe apparent to those of skill in the art.

FIG. 10 shows another method and apparatus for thermal renalneuromodulation via direct application of thermal energy to the targetneural fibers. The apparatus 340 comprises renal artery cuff 342 havingone or more integrated thermoelectric elements that are electricallycoupled to an internal or external power supply 344. The thermoelectricelement utilizes the well-known Peltier effect (i.e., the establishmentof a thermal gradient induced by an electric voltage) to achieve thermalrenal neuromodulation.

An electric current is passed from the power supply to thethermoelectric element, which comprises two different metals (e.g., ap-type and an n-type semiconductor) that are connected to each other attwo junctions. The current induces a thermal gradient between the twojunctions, such that one junction cools while the other is heated.Reversal of the polarity of the voltage applied across the two junctionsreverses the direction of the thermal gradient.

Either the hot side or the cold side of the thermoelectric element facesradially inward in order to heat or cool, respectively, the targetneural fibers that travel along the renal artery to achieve thermalrenal neuromodulation. Optionally, the radially outward surface of thethermoelectric element may be insulated to reduce a risk of thermaldamage to the non-target tissues. The cuff 342 may comprise one or moretemperature sensors, such as thermocouples, for monitoring thetemperature of the target neural fibers and/or of the non-targettissues.

FIG. 11 shows another method and apparatus utilizing the Peltier effect.The apparatus 350 comprises an implanted or external pump 352 connectedto a renal artery cuff 354 via inlet fluid conduit 356 a and outletfluid conduit 356 b. The inlet fluid conduit transfers fluid from thepump to the cuff, while the outlet fluid conduit transfers fluid fromthe cuff to the pump to circulate fluid through the cuff. A reservoir offluid may be located in the cuff, the pump and/or in the fluid conduits.

The pump 352 further comprises one or more thermoelectric or otherthermal elements in heat exchange contact with the fluid reservoir forcooling or heating the fluid that is transferred to the cuff tothermally modulate the target neural fibers. The apparatus 350optionally may have controls for automatic or manual control of fluidheating or cooling, as well as fluid circulation within the cuff.Furthermore, the apparatus may comprise temperature and/or renalsympathetic neural activity monitoring or feedback control. Although theapparatus illustratively is shown unilaterally treating neural fibersinnervating a single kidney, it should be understood that bilateraltreatment of neural fibers innervating both kidneys alternatively may beprovided.

Thermal renal neuromodulation alternatively may be achieved viahigh-intensity focused ultrasound, either pulsed or continuous. Highintensity focused ultrasound also may induce reversible or irreversibleelectroporation in the target neural fibers. Furthermore, the ultrasoundmay be delivered over a full 360° (e.g. when delivered intravascularly)or over a radial segment of less than 360° (e.g., when deliveredintravascularly, extravascularly, intra-to-extravascularly, or acombination thereof). In FIG. 12, the apparatus 360 comprises a catheter362 having ultrasound transducers 364 positioned along the shaft of thecatheter within an inflatable balloon 366. The ultrasound transducersare coupled to an ultrasound signal generator via conductors 365. Theballoon comprises an acoustically reflective portion 368 of a surface ofthe balloon for reflecting an ultrasound wave, as well as anacoustically transmissive portion 369 of the surface for passage of thewave through the balloon. In this manner, the wave may be focused asshown at a focal point or radius P positioned a desired focal distancefrom the catheter shaft. In an alternative embodiment, the transducersmay be attached directly to the balloon.

The focal distance may be specified or dynamically variable such that,when positioned within a blood vessel, the ultrasonic wave is focused ata desired depth on target neural fibers outside of the vessel. Forexample, a family of catheter sizes may be provided to allow for a rangeof specified focal distances. A dynamically variable focal distance maybe achieved, for example, via calibrated expansion of the balloon.

Focusing the ultrasound wave may produce a reverse thermal gradient thatprotects the non-target tissues and selectively affect the target neuralfibers to achieve thermal renal neuromodulation via heating. As aresult, the temperature at the vessel wall may be less than thetemperature at the target tissue. FIG. 12A shows the apparatus 360 in areduced delivery and retrieval configuration, while FIG. 12B shows theapparatus in an expanded deployed configuration. FIG. 13 shows analternative embodiment of the apparatus 360 wherein the ultrasoundtransducers 364′ are concave, such that the ultrasound signal isself-focusing without need of the reflective portion of the balloon 366(e.g., the balloon may be acoustically transmissive at all points).

The apparatus described above with respect to FIGS. 3-13 optionally maybe used to quantify the efficacy, extent or cell selectivity ofthermally-induced renal neuromodulation in order to monitor and/orcontrol the neuromodulation. As discussed previously, the apparatus mayfurther comprise one or more sensors, such as thermocouples or imagingtransducers, for measuring and monitoring one or more parameters of theapparatus, of the target neural fibers and/or of the non-target tissues.For example, a temperature rise or drop above or below certainthresholds is expected to thermally ablate, non-ablatively injure,freeze or otherwise damage the target neural fibers, thereby modulatingthe target neural fibers.

FIGS. 14A and 14B classify the various types of thermal neuromodulationthat may be achieved with the apparatus and methods of the presentinvention. FIGS. 14A and 14B are provided only for the sake ofillustration and should in no way be construed as limiting. FIG. 14Aclassifies thermal neuromodulation due to heat exposure. As shown,exposure to heat in excess of a body temperature of about 37° C., butbelow a temperature of about 45° C., may induce thermal injury viamoderate heating of the target neural fibers or of vascular structuresthat perfuse the target fibers. For example, this may inducenon-ablative thermal injury in the fibers or structures. Exposure toheat above a temperature of about 45° C., or above about 60° C., mayinduce thermal injury via substantial heating of the fibers orstructures. For example, such higher temperatures may thermally ablatethe target neural fibers or the vascular structures. Regardless of thetype of heat exposure utilized to induce the thermal neuromodulation, areduction in renal sympathetic nerve activity (“RSNA”) is expected.

As seen in FIG. 14B, thermal cooling for neuromodulation includesnon-freezing thermal slowing of nerve conduction and/or nerve injury, aswell as freezing thermal nerve injury. Non-freezing thermal cooling mayinclude reducing the temperature of the target neural fibers or of thevascular structures that feed the fibers to temperatures below the bodytemperature of about 37° C., or below about 20° C., but above thefreezing temperature of about 0° C. This non-freezing thermal coolingmay either slow nerve conduction or may cause direct neural injury.Slowed nerve conduction may imply continuous or intermittent cooling ofthe target neural fibers to sustain the desired thermal neuromodulation,while direct neural injury may require only a discrete treatment toachieve sustained thermal neuromodulation. Thermal cooling forneuromodulation also may include freezing thermal nerve injury, e.g.,reducing the temperature of the target neural fibers or of the vascularstructures that feed the fibers to temperatures below the freezing pointof about 0° C. Regardless of the type of cold exposure utilized toinduce the thermal neuromodulation (freezing or non-freezing), areduction in renal sympathetic nerve activity (“RSNA”) is expected.

It is expected that thermally-induced renal neuromodulation, whetherdelivered extravascularly, intravascularly, intra-to-extravascularly ora combination thereof, may alleviate clinical symptoms of CHF,hypertension, renal disease, myocardial infarction, atrial fibrillation,contrast nephropathy and/or other cardio-renal diseases for a period ofmonths, potentially up to six months or more. This time period may besufficient to allow the body to heal; for example, this period mayreduce the risk of CHF onset after an acute myocardial infarction,thereby alleviating a need for subsequent re-treatment. Alternatively,as symptoms reoccur, or at regularly scheduled intervals, the patientmay receive repeat therapy.

Although preferred illustrative variations of the present invention aredescribed above, it will be apparent to those skilled in the art thatvarious changes and modifications may be made thereto without departingfrom the invention. It is intended in the appended claims to cover allsuch changes and modifications that fall within the true spirit andscope of the invention.

1. An ultrasound apparatus for thermally-induced renal neuromodulation,the apparatus comprising: a catheter configured for intravascularplacement within a renal blood vessel of a human patient; and one ormore ultrasound transducers positioned along the catheter, wherein theone or more ultrasound transducers are configured to transmit ultrasoundwaves to renal neural fibers outside of the vessel to achieve thermalrenal neuromodulation via heating.
 2. The apparatus of claim 1, furthercomprising an inflatable balloon proximate to the one or more ultrasoundtransducers, wherein the apparatus is configured to vary between areduced delivery and retrieval configuration and an expanded deployedconfiguration.
 3. The apparatus of claim 2 wherein the one or moreultrasound transducers are positioned within the inflatable balloon. 4.The apparatus of claim 2 wherein the one or more ultrasound transducersare attached directly to the inflatable balloon.
 5. The apparatus ofclaim 2 wherein the inflatable balloon comprises an acousticallytransmissive portion through which the ultrasound waves passes.
 6. Theapparatus of claim 2 wherein the inflatable balloon comprises anacoustically reflective portion for reflecting the ultrasound waves. 7.The apparatus of claim 2 wherein calibrated expansion of the inflatableballoon dynamically varies a focal distance of the ultrasound waves. 8.The apparatus of claim 1 wherein the one or more ultrasound transducersare configured to delivery high intensity focused ultrasound to theneural fibers.
 9. The apparatus of claim 1 wherein the one or moreultrasound transducers comprise a self-focusing concave transducerconfigured to direct the ultrasound waves to a specific focal point. 10.The apparatus of claim 1, further comprising an ultrasound signalgenerator coupled to the one or more ultrasound transducers.
 11. Theapparatus of claim 1, further comprising a temperature sensor.
 12. Theapparatus of claim 11 wherein data from the temperature sensor is usedfor feedback control of the thermal neuromodulation therapy.
 13. Theapparatus of claim 1 wherein the one or more ultrasound transducers areconfigured to focus the ultrasound waves on the neural fibers at adesired depth outside of the vessel.
 14. The apparatus of claim 13wherein a thermal gradient is produced when the ultrasound waves arefocused on the neural fibers outside of the vessel.
 15. The apparatus ofclaim 13 wherein a thermal gradient is produced when the ultrasoundwaves are focused on the neural fibers outside of the vessel such that atemperature at a wall of the vessel is less than a temperature at theneural fibers, and wherein the reverse thermal gradient protectsnon-targeted tissue while selectively affecting the neural fibers. 16.The apparatus of claim 1, further comprising an imaging transducer. 17.The apparatus of claim 1 wherein the catheter further comprises athermal fluid configured to remove excess thermal energy and protectnon-targeted tissues.
 18. The apparatus of claim 17 wherein the catheteris configured to temporarily occlude blood flow in the vessel.
 19. Theapparatus of claim 1 wherein the one or more ultrasound transducers areconfigured to transmit the ultrasound waves over a full 360°.
 20. Amethod for catheter-based renal neuromodulation, the method comprising:positioning a catheter having a therapeutic element within a renal bloodvessel of a human patient and proximate to neural fibers associated withrenal function, wherein the therapeutic element comprises one or moreultrasound transducers positioned along the catheter; and thermallyinhibiting neural activity along the neural fibers via ultrasound energyfrom the therapeutic element.
 21. The method of claim 20 whereinpositioning a catheter having a therapeutic element within a renal bloodvessel comprises intravascularly positioning the catheter having the oneor more ultrasound transducers within a renal artery of the patient. 22.The method of claim 20 wherein thermally inhibiting neural activityalong the neural fiber comprises delivering ultrasound energy via theone or more ultrasound transducers to a renal nerve proximate to a renalartery of the patient.
 23. The method of claim 22 wherein transferringultrasound energy via the one or more ultrasound transducers to therenal nerve of the patient comprises transmitting the ultrasound wavesover a full 360° about the catheter.
 24. The method of claim 20 whereinthermally inhibiting neural activity along the neural fiber comprisesblocking neural traffic to and/or from a kidney of the patient.
 25. Themethod of claim 20 wherein thermally inhibiting neural activity alongthe neural fiber comprises ablating a renal nerve of the patient viaultrasound energy from the one or more ultrasound transducers.
 26. Themethod of claim 20 wherein the catheter comprises an inflatable balloonproximate to the one or more ultrasound transducers, and whereinpositioning a catheter having a therapeutic element within a renal bloodvessel comprises intravascularly delivering the inflatable balloon tothe renal blood vessel in a reduced delivery and retrieval configurationand expanding the balloon to a deployed configuration within the renalblood vessel.